/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.socket.config.annotation;

import java.util.Date;
import java.util.concurrent.ScheduledFuture;

import org.springframework.context.annotation.Bean;
import org.springframework.lang.Nullable;
import org.springframework.scheduling.TaskScheduler;
import org.springframework.scheduling.Trigger;
import org.springframework.scheduling.concurrent.ThreadPoolTaskScheduler;
import org.springframework.web.servlet.HandlerMapping;

/**
 * Configuration support for WebSocket request handling.
 *
 * @author Rossen Stoyanchev
 * @since 4.0
 */
public class WebSocketConfigurationSupport {

    @Nullable
    private ServletWebSocketHandlerRegistry handlerRegistry;

    @Nullable
    private TaskScheduler scheduler;


    @Bean
    public HandlerMapping webSocketHandlerMapping() {
        ServletWebSocketHandlerRegistry registry = initHandlerRegistry();
        if (registry.requiresTaskScheduler()) {
            registry.setTaskScheduler(initTaskScheduler());
        }
        return registry.getHandlerMapping();
    }

    private ServletWebSocketHandlerRegistry initHandlerRegistry() {
        if (this.handlerRegistry == null) {
            this.handlerRegistry = new ServletWebSocketHandlerRegistry();
            registerWebSocketHandlers(this.handlerRegistry);
        }
        return this.handlerRegistry;
    }

    protected void registerWebSocketHandlers(WebSocketHandlerRegistry registry) {
    }

    /**
     * The default TaskScheduler to use if none is configured via
     * {@link SockJsServiceRegistration#setTaskScheduler}, i.e.
     * <pre class="code">
     * &#064;Configuration
     * &#064;EnableWebSocket
     * public class WebSocketConfig implements WebSocketConfigurer {
     *
     *   public void registerWebSocketHandlers(WebSocketHandlerRegistry registry) {
     *     registry.addHandler(myWsHandler(), "/echo").withSockJS().setTaskScheduler(myScheduler());
     *   }
     *
     *   // ...
     * }
     * </pre>
     */
    @Bean
    public TaskScheduler defaultSockJsTaskScheduler() {
        return initTaskScheduler();
    }

    private TaskScheduler initTaskScheduler() {
        if (this.scheduler == null) {
            ServletWebSocketHandlerRegistry registry = initHandlerRegistry();
            if (registry.requiresTaskScheduler()) {
                ThreadPoolTaskScheduler threadPoolScheduler = new ThreadPoolTaskScheduler();
                threadPoolScheduler.setThreadNamePrefix("SockJS-");
                threadPoolScheduler.setPoolSize(Runtime.getRuntime().availableProcessors());
                threadPoolScheduler.setRemoveOnCancelPolicy(true);
                this.scheduler = threadPoolScheduler;
            } else {
                this.scheduler = new NoOpScheduler();
            }
        }
        return this.scheduler;
    }


    private static class NoOpScheduler implements TaskScheduler {

        @Override
        @Nullable
        public ScheduledFuture<?> schedule(Runnable task, Trigger trigger) {
            throw new IllegalStateException("Unexpected use of scheduler.");
        }

        @Override
        public ScheduledFuture<?> schedule(Runnable task, Date startTime) {
            throw new IllegalStateException("Unexpected use of scheduler.");
        }

        @Override
        public ScheduledFuture<?> scheduleAtFixedRate(Runnable task, Date startTime, long period) {
            throw new IllegalStateException("Unexpected use of scheduler.");
        }

        @Override
        public ScheduledFuture<?> scheduleAtFixedRate(Runnable task, long period) {
            throw new IllegalStateException("Unexpected use of scheduler.");
        }

        @Override
        public ScheduledFuture<?> scheduleWithFixedDelay(Runnable task, Date startTime, long delay) {
            throw new IllegalStateException("Unexpected use of scheduler.");
        }

        @Override
        public ScheduledFuture<?> scheduleWithFixedDelay(Runnable task, long delay) {
            throw new IllegalStateException("Unexpected use of scheduler.");
        }
    }
}
